A rack and pinion including a rack and a pinion (or a pinion gear) that mesh with each other is known as a conversion device between rotary motion and linear motion. The rack and pinion is used in mechanical devices such as a conveying device, an industrial robot, a machine tool, or a precision machine that require high efficiency, high accuracy, long life, and high driving force transfer.
The rack and pinion generally has a gap called backlash between rack teeth and pinion teeth to avoid jamming of the teeth. However, with the backlash, even if the pinion is stopped, the pinion having inertia moves by an amount of the backlash, thereby reducing positional accuracy in stopping.
Patent Document 1 proposes a conversion device 100 between rotary motion and linear motion that solves the above problem. As shown in FIG. 11, the conversion device 100 converts between rotary motion and linear motion using a rack 105 including teeth 104 having a shape of a plurality of trochoidal curves, and a pinion 107 including a plurality of rollers 106 that mesh with the teeth 104. Each tooth 104 has such a shape that a bottom of the tooth substantially forms an arc having a diameter larger than that of a roller 106 so that a central locus of the roller 106 that meshes with the rack 105 makes a trochoidal curve. The rack 105 and the pinion 107 are preloaded and used. Further, an approach gradually away from an outer locus of the roller 106 is formed at an end of the tooth 104.